The present invention relates to an electronic device for determining the position coordinates of a position indicating implement over a tablet surface.
Digitizing tablet systems are well known in the art and are used in a variety of applications. These systems generally include a tablet, a position indicating implement and associated electronics for producing some form of interaction between the implement and the tablet from which is derived digital data signals representing the position of the implement on the tablet.
A number of these systems employ a tablet having a grid of individual loops, one set of loops being aligned for indicating position in one coordinate direction and a second set of loops positioned for determining position in a second coordinate. One example of such a system is described in U.S. Pat. No. 4,644,102 (Blesser, et al.). Here, each loop is a discrete sensor for sensing the intensity of the current or voltage induced by the coil or coils of the position indicating implement. The system takes advantage of the basic magnetic equations which relate the field intensity of the induced current to the location of the electric coils. Generally the intensity will be in the form of a parabola in the region of interest. One determines the location of the coils by determining the intensity of the current sensed in the parallel conductive loops.
A second method commonly used for forming the grid on a digitizing tablet is described in U.S. Pat. No. 3,647,963 (Bailey). Bailey described the use of a pair of grids for each position coordinate. A grid included an outer loop which surrounds the tablet surface and a circuitous conductive line which extends from one corner of the outer loop to an opposite corner of the loop. The conductive line circuitously winds its way back and forth across the digitizing tablet forming a series of parallel conductive loop regions. An output signal is taken from a lead attached to the outer loop and a second lead attached to the circuitous conductive line. By offsetting two of such grids in each the X and Y directions, sufficient information can be gathered to identify the position of an electric coil in two dimensions.
In the art of digitizing tablets, generally, variations in spatial relationships are achieved through altering the design of the grid sense system. It is an object of the present invention to produce different spatial geometries, which in many cases are not physically achievable using the old methods, through the use of linear spatial filters on the signals from a single tablet design.
It is a further object of the present invention to provide a digitizing tablet which determines position of the tip of a position indicating stylus having an electric coil despite tilting of the stylus. It is a still further object of the present invention to measure and report the tilt of the stylus.